Dawsonite-type precursors for catalytic Al, Cr, and Fe oxides: Synthesis and characterization

Preparation of dawsonite-type compounds, NH4M(CO3)(OH)(2), was attempted for M = Al., Cr, or Fe, using a hydrothermal method under various basicity and thermal conditions. Crystalline structure and chemical composition verification studies, employing X-ray diffractometry, infrared spectroscopy, and elemental analyses, revealed that a successful preparation is critically dependent on the availability of MO(OH)(-) and HCO3- reaction species, which is facilitated at pH value in the vicinity of 10 and temperature <= 100 degrees C. Accordingly, it was possible to prepare dawsonite-type Compounds for Al and Cr, but not for Fe. In the latter case, the sparingly soluble FeOOH compound was the eventual product. Thermal analyses of the hydrothermal products helped define the temperature regime at which they decompose into the corresponding M(III)-oxides. Bulk and surface characterization studies of the oxides thus produced revealed that dawsonite-type compounds are feasible precursors for catalytic-grade Al2O3 and Cr2O3.